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January 17, 2014
By Barry Schiff
“Once you have tasted flight, you will forever walk the Earth with your eyes turned skyward, for there you have been, and there you will always long to return.”
Although this beautiful piece of prose is well known to pilots, it could not have been meant for us. When written by Leonardo da Vinci some 500 years ago, there were no pilots. Perhaps the Italian master of the Renaissance was imagining what flight would or could be like. More likely, he was inspired by the flight of birds (of which there are more than 10,000 species.)
When man (both genders) observed that birds had wings, he was jealous and tried for centuries to emulate them. He might have been most envious of the peregrine falcon, speediest in the avian world. Clocked in a 45-degree dive at 217 mph, it can outrun most lightplanes operating at redline. Think of how embarrassing it would be to be passed by a bird (or to experience a bird strike from behind). Clocked at 106 mph, the spine-tailed swift is the fastest in level, wing-flapping flight.
Can birds stall? Yes, they can and do, but only during a wind shear encounter. Unlike their human counterparts, though, they recover instinctively and immediately. Although the vast majority of birds lift off from a standstill, a few cannot. Like an airplane, a buzzard, for example, requires a takeoff run.
The heaviest bird is the great bustard. It typically grosses at 40 to 42 pounds, although one reportedly got too heavy (46.3 pounds) and paid the ultimate price. Someone in northeastern China shot the poor bustard as it attempted to escape during an overweight takeoff. Some pilots suffer equally fatal consequences when operating at excessive weights.
The largest birds aren’t bustards. The wandering albatross has a wing span of up to 12 feet. An outstanding glider, it can remain aloft for hours without beating its wings. and even sleeps while flying.
The smallest and lightest bird obviously is the hummingbird, the grand champion of aerobatics. No other bird can hover and fly backwards, sideways, and—yes—even inverted for short periods. Like other birds, these tiny, angelic creatures can withstand a greater load factor than a human pilot because they do not fly with their head above their hearts. A small hummingbird weighs about the same as a penny. The bee hummingbird is the lightest and weighs the same as two paperclips (about 2 grams).
The world’s avian altitude record apparently is held by a Rüppell’s vulture, but it did not survive to brag about it. Nor was it squawking the appropriate transponder code when it collided with a Boeing jetliner over the Ivory Coast at Flight Level 410. Bar-headed geese routinely fly over the Himalayas and Mt. Everest (29,000 feet) while migrating.
Wilbur Wright was first to report a bird strike, and Cal Rodgers, first to fly across the United States, was first to be killed by a bird when a seagull jammed the controls of his biplane.
Lowering altitude somewhat, birds have been taking advantage of ground effect to reduce induced drag long before man took to the sky. Sea ducks, pelicans, sandpipers, and others routinely follow the contours of waves and swells at a height less than their wingspans to improve performance.
According to the Audubon Society, birds are VFR creatures and do not intentionally fly into clouds. They have more common sense than some pilots and ground themselves on foggy days. (Small birds occasionally do get caught in IMC and fly into tall buildings, as do some pilots.)
If birds really do attempt to avoid flying in cloud, then one of the great mysteries of bird flight involves the bar-tailed godwit, a long-range flier without equal. This shorebird migrates diagonally across the Pacific Ocean, all the way from Alaska to New Zealand. It covers these 7,000 miles in four to six days without stopping for rest or nutrition, a miracle unto itself. But flying this route inevitably must require it to cross the intertropical convergence zone, a band of thunderstorms encircling the Earth. What do godwits do upon encountering a line of thunderstorms? There’s no place out there to land, and a route deviation increases the fatigue associated with such a marathon flight. Do godwits and other birds fly beneath thunderstorms? They obviously fly in rain, but how do they cope with hail and microbursts?
Also, what happens when a bird flies through freezing rain? Can it be taken down by structural icing? No one seems to know.
We have been taught much by the flight of birds, but there is much more to learn, which is why we continue to observe them with awe and envy.
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